Nonresonant diaphragm



July 26,1927. 1,637,243

E. REISZ NONRESONANT DIAPHRAGM Filed Dec. 1. 1926 Patented July 26,1927.

UNITED STATES EUGEN BEISZ, OI BEBLIN-DAHLEK, GERMANY.

HONBESONANT DIAPHRAGK.

Application filed December 1, 1928, Serial No. 152,028, and in GermanyNovember 18, um.

This invention relates to a non-resonant diaphragm which is adapted foruse in electric microphones and receivers generally and which permitsthe tone values of spoken words or music to be transmitted in a mannerwhich is extremely natural.

The invention consists essentially in the fact that carbon granules ofvarious sizes are stuck down onto a thin and unstretched skin of rubberor like material, said anules not being mutually united by the adhesivemedium.

An example of a diaphragm constructed according to my invention isillustrated on the drawing in which Figure 1 is a diagrammatical view invertical section,

Figure 2 shows a microphone provided with my improved diaphragm.

To an unstretched or only slightly stretched rubber skin a (Figure 1) ofabout 0,1 millimetres of thickness, carbon granules b of various degreesof coarseness are applied and are afiixed to the rubber skin by means ofan adhesive medium (rubber solution, for instance). This may be suitablyeffected by first of all spreading rubber solution over the rubber skin,while the latter is maintained in a stretched condition. and thensprinkling the carbon granules thereupon. After the rubber solution hasdried, the rubber skin is released from tension and stuck onto a metalring a in such manner that the layer of carbon granules is conductivelyconnected to the said metal ring.

Such a diaphragm oscillates without any particular frequency beingaccentuated, a phenomenon which is attributable to the fact that theindividual carbon granules can oscillate independently of each other.Since, moreover, the carbon granules are of various sizes, they thusprovide a. very large number of oscillating elements of which thenatural periods of oscillation differ materially one from another. Theperiod of oscillation of such an element, that is to say, a carbongranule in combination with the corresponding rubber surface about 0,5millunetres of diameter, is proportional to where m is the mass and fthe stiffness factor of the small rubber surface. Since m is very smalland f very large, the very small area of diaphragm under considerationmust necessarily have an oscillation period of verv small value, forexample, 1/8000 second.

As stated above, it is important that the carbon granules be stuck onlyto the rubber skin and that they do not stick together. If. forinstance, the carbon granules on the rubber skin were given anadditional or superficial coating of rubber solution, so as to deprivethem of their independent movement, the diaphragm would no longerfunction without resonance.

Figure 2 shows amicrophone provided with the diaphragm of this inventionThe carbon granule layer 6, stuck to the rubber skin a bears, throughthe medium of an interposed layer f of granulated carbon, upon a fixedcarbon block 9, supported upon a fixed and vibrationless base 72..

The pulverulent conductor 6 may either consist of carbon granules or offinely powdered metal. Care must be taken, however, that the individualparticles are only very loosely connected in order to avoid soundfigures in the diaphragm.

I claim:

1. A non-resonant diaphragm, characterized by the fact that carbongranules of various sizes are stuck onto thin unstretched skin ofnon-resonant material, said granules being disconnected from each other.

2. A microphone having a diaphragm according to claim 1, characterizedin that the carbon granule covered skin, through the medium of anothermass of granulated carbon, bears upon a fixed carbon block supportedupon'a vibrationless base member.

3. A non-resonant diaphragm accord ng to claim 1, characterized in thatthe ulverulent conductor is applied to a very t 'n and elasticinsulating layer, for instance a rubber skin.

4. A non-resonant diaphragm, comprising a thin iece of elastic materialhaving finely reduce conducting material secured to one face with theparticles thereof disconnected from each other.

5. A non-resonant diaphragm, comprising a thin piece of elastic materialhaving anulated carbon secured to one face not the granules 0i carbondisconnected from each other.

6. A non-resonant diaphragm, comprising a thin piece of rubber or likematerial having carbon granules secured on the entire surface of oneface with the granules disconnected from each other, and a metallic rinto which the piece of rubber is secured wit the granules of carbonengaiing said ring.

In testimony whereof I ave signed my name to this specification.

EUGEN REISZ.

